How to widen header image in Genesis/Foodie Pro

Hi, I hope someone can help. I am have searched and searched but can’t find what I’m looking for (although it’s possible that there are some CSS help that I’m not if it’s what I need!).

I am trying to add a header image to my site (https://www.whatannabelcooks.com). I can upload the image ok but the image doesn’t ‘fill’ the width of the space. What’d like is for the header image to fill the width of the site ie be in line with width of the page. I’ve tried playing around with pixel sizes but doesn’t seem to help. I’ll leave it up for now so you can see what it looks like as i can’t work out how to post a screen shot in this box!

I am using Foodie Pro which is a Genesis child theme.

thanks in advance,
Annabel